package homework;

import java.util.*;

public class BinaryTree {

    static class TreeNode {
        public char val;
        public TreeNode left;//左孩子的引用
        public TreeNode right;//右孩子的引用

        public TreeNode(char val) {
            this.val = val;
        }
    }


    /**
     * 创建一棵二叉树 返回这棵树的根节点
     *
     * @return
     */
    public TreeNode createTree() {
        TreeNode A = new TreeNode('A');
        TreeNode B = new TreeNode('B');
        TreeNode C = new TreeNode('C');
        TreeNode D = new TreeNode('D');
        TreeNode E = new TreeNode('E');
        TreeNode F = new TreeNode('F');
        TreeNode G = new TreeNode('G');
        A.left = B;
        A.right = C;
        B.left = D;
        B.right = E;
        C.left = F;
        F.right = G;
        return A;
    }

    // 前序遍历
    public void preOrder(TreeNode root) {
        if(root == null){
            return;
        }
        System.out.print(root.val + " ");
        preOrder(root.left);
        preOrder(root.right);
    }

    // 中序遍历
    void inOrder(TreeNode root) {
        if(root == null){
            return;
        }
        preOrder(root.left);
        System.out.print(root.val + " ");
        preOrder(root.right);
    }

    // 后序遍历
    void postOrder(TreeNode root) {
        if(root == null){
            return;
        }
        postOrder(root.left);
        postOrder(root.right);
        System.out.print(root.val + " ");
    }

    public static int nodeSize;

    /**
     * 获取树中节点的个数：遍历思路
     */
    void size(TreeNode root) {
        if(root == null){
            return;
        }
        nodeSize++;
        size(root.left);
        size(root.right);
    }

    /**
     * 获取节点的个数：子问题的思路
     *
     * @param root
     * @return
     */
    int size2(TreeNode root) {
        if(root == null){
            return 0;
        }
        return size2(root.left) + size2(root.right) + 1;
    }


    /*
     获取叶子节点的个数：遍历思路
     */
    public static int leafSize = 0;

    void getLeafNodeCount1(TreeNode root) {
        if(root == null){
            return;
        }
        if(root.left == null && root.right == null){
            leafSize++;
        }
        getLeafNodeCount1(root.left);
        getLeafNodeCount1(root.right);
    }

    /*
     获取叶子节点的个数：子问题
     */
    int getLeafNodeCount2(TreeNode root) {
        if(root == null){
            return 0;
        }
        if(root.left == null && root.right == null){
            return 1;
        }
        return getLeafNodeCount2(root.left) + getLeafNodeCount2(root.right);
    }

    /*
    获取第K层节点的个数
     */
    int getKLevelNodeCount(TreeNode root, int k) {
        if(root == null){
            return 0;
        }
        if(k == 1){
            return 1;
        }
        return getKLevelNodeCount(root.left, k - 1) +
                getKLevelNodeCount(root.right, k - 1);
    }

    /*
     获取二叉树的高度
     时间复杂度：O(N)
     */
    int getHeight(TreeNode root) {
        if(root == null){
            return 0;
        }
        int leftHeight = getHeight(root.left);
        int rightHeight = getHeight(root.right);

        return 1 + (leftHeight > rightHeight ? leftHeight : rightHeight);
    }


    // 检测值为value的元素是否存在
    TreeNode find(TreeNode root, char val) {
        if(root == null){
            return null;
        }
        if(root.val == val){
            return root;
        }
        TreeNode ret = find(root.left, val);
        if(ret != null){
            return ret;
        }
        ret = find(root.right, val);
        if(ret != null){
            return ret;
        }
        return null;
    }

    public boolean isSameTree(TreeNode p, TreeNode q){
        if((p != null && q == null) || (p == null && q != null)){
            return false;
        }
        if(p == null && q == null){
            return true;
        }
        if(p.val != q.val){
            return false;
        }
        return isSameTree(p.left, q.left) && isSameTree(p.right, q.right);
    }

    public boolean isSubTree(TreeNode root, TreeNode subTree){
        if(root == null){
            return false;
        }
        if(isSameTree(root, subTree)){
            return true;
        }
        if(isSameTree(root.left, subTree)){
            return true;
        }
        if(isSameTree(root.right, subTree)){
            return true;
        }
        return false;
    }

    //层序遍历
    public void levelOrder(TreeNode root) {
        //层序遍历需要用到队列（因为层序是先进先出）
        Queue<TreeNode> queue = new LinkedList<>();
        queue.offer(root);
        while(!queue.isEmpty()){
            TreeNode cur = queue.poll();
            System.out.print(cur.val + " ");
            if(cur.left != null){
                queue.offer(cur.left);
            }
            if(cur.right != null){
                queue.offer(cur.right);
            }
        }
    }

    public List<List<TreeNode>> levelOrder2(TreeNode root) {
        if(root == null){
            return null;
        }
        List<List<TreeNode>> levelList = new ArrayList<>();
        //层序遍历需要用到队列（因为层序是先进先出）
        Queue<TreeNode> queue = new LinkedList<>();
        queue.offer(root);
        while(!queue.isEmpty()){
            int size = queue.size();//2
            List<TreeNode> nodeList = new ArrayList<>();
            while(size > 0){
                TreeNode cur = queue.poll();
                nodeList.add(cur);
                size--;
                if(cur.left != null){
                    queue.offer(cur.left);
                }
                if(cur.right != null){
                    queue.offer(cur.right);
                }
            }
            levelList.add(nodeList);
        }
        return levelList;
    }


    // 判断一棵树是不是完全二叉树
    boolean isCompleteTree(TreeNode root) {
        if(root == null){
            return true;
        }
        Queue<TreeNode> queue = new LinkedList<>();
        queue.offer(root);
        while(!queue.isEmpty()){
            TreeNode cur = queue.poll();
            if(cur != null){
                queue.offer(cur.left);
                queue.offer(cur.right);
            }else{
                break;
            }
        }
        while(!queue.isEmpty()){
            if(queue.poll() != null){
                return false;
            }
        }
        return true;
    }

    //二叉树的后序非递归遍历
    public List<TreeNode> postOrderNor(TreeNode root){
        List<TreeNode> list = new ArrayList<>();
        if(root == null){
            return list;
        }
        Stack<TreeNode> stack = new Stack<>();
        TreeNode cur = root;
        TreeNode top = null;
        TreeNode prev = null;
        while(cur != null || !stack.isEmpty()){
            while(cur != null){
                stack.push(cur);
                cur = cur.left;
            }
            top = stack.peek();
            if(top.right == null || top.right == prev){
                top = stack.pop();
                list.add(top);
                prev = top;
            }else{
                cur = top.right;
            }
        }
        return list;
    }
}